1. Field of the Invention
The present invention relates to a magnetic recording medium having a running stability and more particularly, it is concerned with a magnetic recording tape suitable for short wavelength recording and having a decreased coefficient of friction.
2. Description of the Prior Art
Of late, high density recording has been desired in magnetic recording tapes, in particular, video tapes and, according to the improvement of the properties of magnetic recording layers, the recording wavelength has been decreased from 6 microns to 2 microns and the supply speed of a tape has also been decreased from 38 cm/sec to 7.5 cm/sec. On the other hand, the change of a tape caused by temperature, frictions, etc. has not been neglected with the progress of high density recording. In comparison of the cases wherein the tape supply speed is 38 cm/sec and the recording wavelength is 4 microns and wherein the tape supply speed is 3 cm/sec and the recording wavelength is 2 microns, for example, the latter case requires a better surface property of a tape than the former case, thus resulting in that a tape stickslip and running unevenness tend to occur readily.
In the magnetic tapes of the prior art, (1) the base surface side is not treated, (2) has a back coat layer consisting mainly of carbon black and (3) is coated with a lubricant such as graphite or molybdenum disulfide as in endless tapes.
The magnetic tape of the type (1) has predominantly been used at present, which has, howwever, the problem that due to the exposed support base, the coefficient of friction is increased when the relative speed of the tape is decreased, the tape tends to be scratched at a guide pole section and many drop outs take place.
The magnetic tape of the type (2) has been used in video tapes for broadcasting, video tapes for business, etc. for the purpose of improving the winding state of the tape, in particular, art a high tape speed supply, which has, however, the problem that because of having an inorganic pigment in the back coat layer, there is a surface roughness causing deterioration of short wavelength signals and increase of noises, the surface roughness of the back coat is transferred to the magnetic layer during storage resulting in increase of noises with the passage of time and a tape path is often abraded by the back layer.
The magnetic tape of the type (3) has been used for the purpose of lowering the coefficient of friction between the magnetic layer and the opposite layer thereto as in an endless tape of Lear Jet type, which has, however, the problem that, as in the case of the above described type (2), there are deterioration of short wavelength signals and increase of noises.